JNC & AD2W Operand Clarity

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JNC & AD2W Operand Clarity

Unread postby decipha » Thu Jul 12, 2018 3:49 pm

i was just ripping through gufb and I noticed something that caught my attention.

Code: Select all
<---PT Dashpot Code--->
5b76: a3,f4,60,42       ldw   R42,[Rf4+60]   tmp8l = DELHYS;
5b7a: 67,72,a6,42       ad2w  R42,[R72+a6]   tmp8l += RATCH;       
5b7e: d3,03             jnc   5b83           if ((uns) tmp8l >= RATCH)  {   // how could this ever be false?


Looks pretty straight forward, DELHYS is loaded to the scratch register. r42 == .06

ratch is then added to it, makes perfect sense thus far. DELHYS + RATCH (1.0) ; r42 == 1.06

then the sum is compared to ratch???

hmm lets see

is 1.06 > or == to 1.00 ??? well yes it is, any 3rd grader can tell you anytime you add a positive number to a positive number you end up with a larger number

considering both are unsigned words how could this ever switch? Looks like a one way ticket to me unless I'm missing something?

only thing i can think is that if the tps fails ratch is set to rativ, perhaps henrys gents didnt know this?

i just looked it up in RZASA and its the exact same code as well although its got the ETC_HP switch mixed in it, otherwise identical
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Re: JNC & AD2W Operand Clarity

Unread postby jsa » Thu Jul 12, 2018 8:49 pm

The addition has not caused a carry, so jump.

The listing is not given correct output.

Which version of SAD did you use?

Is there a jump to L5b7e from somewhere else?
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Re: JNC & AD2W Operand Clarity

Unread postby decipha » Thu Jul 12, 2018 9:56 pm

nope there is no other jumps

the sad i have on the homepage from 2013 its the only one i know of that works

yea that makes sense
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98 Camaro SS - Bounquisha
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03 Marauder - DyShyKy
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Re: JNC & AD2W Operand Clarity

Unread postby jsa » Fri Jul 13, 2018 5:36 am

3.07 is the latest, many bugs fixed.

https://github.com/tvrfan/EEC-IV-disassembler
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